1. Field of the Invention
The present invention relates to a device for inserting a self-expanding stent into a body vessel, with a tube which, in a distal portion, keeps the stent radially compressed, with a pushing element which is guided in the tube and has a proximal end and a distal end, also with a grip that comprises a housing via which the pushing element is secured displaceably on the grip, and also with a stent carrier which is guided in the pushing element and which has a tip which is mounted fixedly on the device via the grip.
2. Related Prior Art
Such devices for insertion of self-expanding stents are known from the prior art. Such insertion systems are used to implant endovascular stents into blood vessels that have been damaged, for example as a result of diseases or the like, or that have had their lumen occluded, as a consequence of which the function of the vessels is greatly impaired. In the prior art, various implantable stent devices are known which, after they have been implanted, keep blood vessels, for example arteries, open. Such stents generally have a tubular body which is inserted into the vessel and is fixed at the relevant location in order to keep the lumen of the vessel open.
Thus, the prior art includes stent grafts, for example, which have a wire framework made of a self-expanding material, and the wire framework can additionally be connected to a tube made of textile.
For implantation, the stent is radially compressed, such that its cross-sectional surface area can be considerably reduced and it can easily be inserted into the vessel. On account of the resiliency of the metal framework, the stent expands back to its original shape and in so doing stretches its jacket surface, which wedges itself internally in the blood vessel.
For implantation, the stents are folded up radially and, with the aid of catheters advanced through the lumen, are then introduced into the blood vessel and placed in the correct position in the vessel. The correct position of the stent can be monitored using X-ray markers, for example. To ensure that the stents remain in the comprised state during their positioning, they are arranged in a sleeve or in a sheath-like tube which, by virtue of its properties, presses the stent radially inwards. This so-called withdrawal sleeve is pulled back after the stent has been positioned in the vessel, in which process the stent is held axially by an abutment element, which is also designated as a pusher. The pusher lies in contact with the stent and holds the latter in its axial position, while the withdrawal sleeve also surrounding the pusher is detached from the stent, which is thus able to expand and wedge itself in the blood vessel.
A very wide variety of stents are used depending on the type of application. The present invention is concerned with the application of what are called braided stents. These are metal stents that are produced by what is called a plain weaving technique. They are composed of a hollow body, which can stretch in the longitudinal direction and whose jacket is a braid made up of a multiplicity of filament-like elements which, in the expanded state of the braided stent, intersect a plane, perpendicular to the longitudinal direction, at a braid angle. A braided stent undergoes a considerable change in length when stretched, this change in length being all the greater the greater the original diameter and the smaller the original braid angle.
For implantation, a braided stent of this type is stored in an elongate configuration in an insertion system or applicator, the latter being introduced percutaneously into the body at a suitable location and being guided through a lumen as far as the vessel where the stent is to be released.
In stents that experience no change or only a very slight change in length when released, the position of the implantable stent can be easily verified, for example using X-ray markers.
In braided (metal) stents, however, a problem that arises is that they grow much shorter when released. The ratio I/L of the stent length I in the loaded state to the free stent length L is dependent on the diameters d in the insertion system and D in the unloaded state and also on the braid angle α:I/L=(D2−d2·cos2 α)1/2/(D·sin α).
For example, when a stent with a length L=40 mm, a diameter D=6 mm and a braid angle α=40° is compressed to a diameter d=1.5 mm in an insertion system, it becomes longer by a factor I/L=1.53. Accordingly, it therefore has a length of 61.2 mm in the insertion system. In a stent with a functional zone, e.g. with a braid angle of α=10°, as is described in patent application DE 103 35 649, for example, the lengthening in the insertion system can even be by a factor I/L=4 to 6.
Braided stents are therefore extremely extensible and, in their elongated state, they as it were store mass which, upon contraction of the stent, ensures a compact and stiff functional area, as is explained in detail in aforementioned DE 103 35 649.
Stents in which this kind of shortening upon release has to be taken into account can no longer be released with precision using the currently existing insertion systems.
For example, the prior art includes insertion systems for stents that experience extreme shortening upon release. In the insertion systems known in the prior art, the problem of shortening is solved by limiting the distal travel of the tip to a few millimeters relative to the sleeve tube. In such insertion systems, the insertion system has to be carefully pulled back at the same time as the stent is being released. This positioning, with millimeter precision, of a braided stent that shortens considerably requires practice on the part of the user and a great deal of experience. The precision and handling characteristics of this system are adapted to the treatment of long peripheral vascular lesions (greater than 3 cm) using suitably long braided stents. For positioning with millimeter precision in short areas of stenosis, as may occur in the internal carotid artery for example, such systems do not afford the required precision.